It is common today for people to carry electronic devices, such as cellphones, wherever they go. These cellphones often facilitate not only phone calls, but also internet use, e-mailing, data storage and retrieval, and the range of functions that in the past were reserved for larger computers. The batteries which power these devices frequently do not have the ability to supply enough energy until the next time that it is convenient to charge the batteries. As a result, there are times when a user must limit her use of the device in order to conserve battery power, and, more seriously, there are times when the user is unable to use the device whatsoever, because the batteries have died.